Recently, as electronic circuits have become highly densified, there are increasing demands to make electronic components that are more compact and have higher performance capabilities. Hence, for example, more compact and larger capacity laminated ceramic capacitors are in high demand.
A laminated ceramic capacitor is embedded with a plurality of opposite internal electrode layers through a dielectric ceramic layer of small thickness inside the ceramic element body. Both sides of the thickness direction of the ceramic element body are covered with outer layer portions, the thickness of which is sufficiently thicker than that of the dielectric ceramic layer (dielectric layer) between the internal electrode layers, and both sides of the longitudinal direction of the ceramic element body are attached with terminal electrodes which are conducted to the internal electrode layers.
For a laminated ceramic capacitor to achieve a small size and a large capacity, methods for increasing the dielectric constant of the dielectric layer, and methods for making the dielectric layer or internal electrode layer and the outer layer portion thinner, have been considered.
However, if the outer layer portion is thinned, there may be problems that when the capacitor is subjected to plating treatment in the process of forming external electrode after firing, or under humidity resistance load test, as water enters inside the element body through a void which exists in the outer layer, degradation of insulating resistance results.
To solve such problems as described above, a method for promoting densification of the outer layer portion appears to be effective. The patent document 1 discloses a technique that after forming the external electrode (terminal electrode) on sintered ceramic body, the entire outer surface is coated with oxide glass to form a glass coat layer, and then the glass coat layer on the outer side of the terminal electrode compared to the electrode coating portion is polished and the surface of the terminal electrode is exposed.
However, this prior art process is a cumbersome and complex, that is, after forming the terminal electrodes in the sintered ceramic body, to form a glass coat layer by coating with oxide glass, and then to polish the glass coat layer on the outer side of the terminal electrode compared to the electrode coating portion, and to make the surface of the terminal electrode exposed. In addition, it is difficult to apply this prior art to small size product.
In patent document 2, a method has been proposed to improve the moisture resistance by filling the oxide compound comprising Mg and Ni as the metal constituting the internal electrode at the boundary portion between the side portion of the internal electrode and the void portion of the side face of the ceramic sintered body.
However, in the case of the above method, it is difficult to improve the moisture resistance while maintaining the dielectric properties due to the diffusion of Mg component into the ceramic element body.
Further, in patent document 3, for the purpose of suppressing the unevenness of sintering between the outer layer portion and the inner layer portion, a manufacturing method of adding the same Ni powder as that covers dielectric body into the ceramic material paste for outer layer portion, is described. However, since Ni has a tendency to diffuse into the dielectric layer during the firing process, there is a problem of the degradation of the electrical properties due to the influence of the diffusion of Ni from the dielectric layers constituting the outer layer portion to the inner layer portion.
In patent document 4, it has been described that the metal portion comprising the same components as the main component of the internal electrode layers exists in an island-like scattered state, in the surrounding portion between the layers where internal electrode layers are provided except the connection end of the internal electrode layers and the external electrodes, whereby the adhesion between the dielectric layers in the surrounding portion where the internal electrode layers are not formed is enhanced, the occurrence of cracks and delaminating can be reduced, and the moisture resistance is improved. However, there is a concern regarding the diffusion of Ni into the inner portion, just as in the case of patent document 3.
The patent document 5 describes a laminated capacitor, that Ni concentration in the dielectric layer of the inner layer portion is controlled to a level lower than that of the outer layer portion, and of the region between the connection ends of the external electrode layers and the internal electrode layers.
The concentration of the Ni diffused into the dielectric in the patent document 5 does not represent the Ni particles segregated in the dielectric layer. Moreover, the Ni is not distributed unevenly as described in the sample of the Experimental Example of patent document 5.